The invention relates to a piston ring, and in particular a compression piston ring.
The running surfaces of piston rings, and in particular of compression piston rings, in internal combustion engines experience a particularly high load at the ring joint end faces, as a result of thermal and mechanical stress. In general, this results in excessive wear and potentially in thermal overload with ensuing seizing. This location in the piston ring constitutes a key weak area in terms of the service life of the piston ring.
The running surfaces of piston rings are frequently provided with hard coatings. However, these generally cannot prevent the partial phenomenon. The ring shape can be optimized in a way that minimizes the joint pressure so as to provide relief at the joint end faces.
Examples of such measures are described as follows:
DE 41 40 232° C.1 discloses a self-tensioning piston ring having a non-uniform radial pressure distribution. The piston ring, when tensioned to the nominal diameter, has a radius of curvature that corresponds to the cylinder radius at the joint end faces in the region α<25°. The radius of curvature is smaller than the cylinder radius in the angle region β=25 to 35° on both sides of the ring joint so that the radial pressure distribution at the joint end faces is virtually zero, but is in excess of 200% of the mean radial pressure in the angle region β=25 to 35°.
DE 36 12 456 A1 describes a piston ring, in which design measures in the ring joint region make pressure equalization via the lower flank more difficult, and wherein the joint end faces are pressed against the lower flank, optionally by way of additional spring elements or by a separate spring-like configuration, in a direction opposite the force of inertia.
DE 100 41 802 C1 describes a compression piston ring, which has a reduced cross-sectional area at the ring circumference, wherein the ring circumference of the compression piston ring is divided into four quadrants. When the one end face is positioned in the first quadrant and the other end face is positioned in the fourth of the imaginary quadrants, the respective reduced cross-sectional area is located exclusively in the first and fourth quadrants, on both sides of the ring joint, and more particularly in the circumferential region in the vicinity of the joint as seen across the entire ring height wherein, once again, the same radial wall thickness as in the region of the ring back is present in the joint region.
DE 10 2007 007 962 B3 discloses a piston ring, comprising a main body that has a running surface provided with a recess, an upper and a lower flank surface, and an inner circumferential surface, wherein at least the recess is provided with at least one wear protection layer and a PVD (physical vapor deposition) topcoat is applied to at least a portion of the running surface, so that the main body, in the finished state thereof, has the PVD topcoat only in the edge region, which is to say outside the recess.